linux-kernel - Re: [PATCH 2/3] objtool: Ignore retpoline alternatives

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Message-ID: <20180111164424.GN3040@hirez.programming.kicks-ass.net>
Date:   Thu, 11 Jan 2018 17:44:24 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Josh Poimboeuf <jpoimboe@...hat.com>
Cc:     David Woodhouse <dwmw2@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Andi Kleen <ak@...ux.intel.com>, Paul Turner <pjt@...gle.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Kees Cook <keescook@...gle.com>,
        Andy Lutomirski <luto@...capital.net>,
        Jiri Kosina <jikos@...nel.org>, gnomes@...rguk.ukuu.org.uk
Subject: Re: [PATCH 2/3] objtool: Ignore retpoline alternatives

On Thu, Jan 11, 2018 at 10:33:26AM -0600, Josh Poimboeuf wrote:
> On Thu, Jan 11, 2018 at 04:27:38PM +0000, David Woodhouse wrote:
> > On Wed, 2018-01-10 at 19:48 -0600, Josh Poimboeuf wrote:
> > > 
> > > +#define ANNOTATE_NOSPEC_ALTERNATIVE                            \
> > > +       "999:\n\t"                                              \
> > > +       ".pushsection .discard.nospec\n\t"                      \
> > > +       ".long 999b - .\n\t"                                    \
> > > +       ".popsection\n\t"
> > > +
> > 
> > <mode name="peterz">
> >   Ick, numbers. Use .Lfoo_%= instead.
> > </mode>
> 
> I seem to recall that not working with inline asm, maybe old versions of
> GCC don't like it or something?  I can try it and see if 0-day bot
> complains.

Note that we'll raise the GCC limit to 4.5 soon to mandate asm-goto, for
x86 at least.